This invention relates to a method of manufacturing a blade or vane for a gas turbine engine and to a core suitable for use in this method.
In the investment casting process it is common to use a core, usually made of a ceramic material, which is held in the mould while the casting is made and whose exterior surface defines the interior surface of a cavity within the finished casting. Such cores are normally subsequently leached out or otherwise removed from the casting to leave the desired cavity. In certain castings, e.g. those which form the cooled blades or vanes in a gas turbine engine, the shape of the internal cavity becomes highly complex and must be very accurate. In these cases, the core itself is normally made as an injection moulding using a split die in two or more pieces which assemble together.
However because the split die technique requires that all projections on the die, and hence cavities in the core, extend or are tapering in the direction of die withdrawal, considerable constraint has been placed on the shape of core which can be made. This has lead to the necessity to form the interior cavity of cooled gas turbine blades or vanes by a combination of casting, machining and fabrication techniques which has increased the cost of the finished product to a considerable degree.
The present invention provides a method of making a blade or vane for a gas turbine engine using a core whose shape is less subject to the limitations imposed by the prior art coremaking process.